1. Field of Use
The present invention generally relates to methods and mechanisms for conducting internetwork communications. More particularly, the present invention relates to methods and mechanisms used by a computer system which executes application programs originally developed to run on another computer system and provides network facilities to carry out communications over a network with other computer systems.
2. Related Art
With the advent of open system platforms which operate under the control of versions of the UNIX operating system, it becomes more and more desirable to be able to efficiently run application programs developed for earlier computer systems, such as proprietary based systems on such open systems without having to rewrite or port such application programs. A computer system which accommodates such application programs is described in related copending patent application of Richard S. Bianchi, Dennis R. Flynn, Marcia T. Fogelgren, Richard A. Lemay, Mary E. Tovell and William E. Woods entitled, "Executing Programs of a First System on a Second System".
Generally, such application programs are required to operate in conjunction with and communicate with other computer systems over internetworks. Many of these computer systems utilized standard communication network protocols, such as TCP/IP, which are normally implemented as part of the computer system's operating system (i.e. kernel). Also, such computer systems generally support multiuser environments in which it was possible for more than one user process at a time to be using such networking facilities. To implement this, the communication protocol implementation required the adoption of a method for identifying the data associated with each user process. That is, when a client process wanted to contact a server process, such as FTP or Telenet, the client process must have a way of identifying the server process that it wants to use. In TCP/IP, if the client process knows the 32 bit Internet address of the host computer on which the server resides, it can contact that host. But, the client process must still have some way of identifying that particular server process.
To solve this problem, the TCP protocol defined a group of well-known ports or well-known addresses which identify the well-known services that a host computer can provide. For example, most TCP/IP implementations provide a file transfer server named FTP that a client process can utilize to transfer a file via a network to another computer system. The 16 bit integer port established for FTP is 21 (decimal). Thus, every TCP/IP implementation that supports FTP, must assign the well-known port of 21 (decimal) to that server.
While this solved the problem of identifying well-known services, the utilization of this convention creates problems where a computer system which implements TCP/IP and supports FTP is required to run multiple well-known port multiple application programs associated with different operating systems components which share a common host communications protocol stack. Here, the well-known application programs associated with the different operating system components, such as those of an emulator and host system are both required to utilize the same identical well-known ports in identifying like application program services. This gives rise to a naming conflict between the different application program services.
Relative to problems relating to process migration, one author has observed that support for process migration is a characteristic that is increasingly important. Protocols such as OSI, X.25 and TCP/IP that use such machine addresses to identify processes make migration difficult because a process cannot take its address with it when it moves. The author describes the use of a new custom protocol called a Fast Local Interact Protocol (FLIP) and an architecture which permits servers to migrate to new machines without requiring any manual reconfiguration, such as TCP/IP requires. For further information regarding this protocol, reference may be made to a section 14.5 entitled "Communication in Amoeba" of the text entitled "Modern Operating Systems" by Andrew S. Tanenbaum published by Prentice-Hall, Inc., copyright 1992. One problem noted relative to this solution is that the new protocol requires considerable changes to be made to a host system. Hence, this approach is not practical where it is essential that the host computer system's operating system remain intact.
Another approach which has been considered is to provide duplicate communication facilities wherein a separate TCP/IP protocol stack and separate hardware facilities are provided for servicing the network demands of two distinct sets of well-known port application programs. While this solution may be satisfactory in terms of eliminating the naming conflict, it would create considerable processing delays causing application programs executing under control of an emulator to run too slow resulting in decreased overall system performance. Also, this approach is too costly in terms of system resources and is unable to take direct advantage of existing host facilities.
Accordingly, it is a primary object of the present invention to provide a method and system which enables application programs running in under control of different operating system components sharing a common communications protocol stack to utilize well-known ports for identifying like protocol application program services.
It is another object of the present invention to provide a method and system for executing application programs which share a common communications protocol stack to utilize well-known port addresses for designating well-known application programs accessible by client application programs on a remote host system which is transparent to the remote system and requires minimal change to the host system thereby facilitating debugging, modifying and maintaining of such application programs.